1. Field of the Invention
The present invention generally relates to a transmitter and method thereof for the transmission of data signals over a transmission line, and more particularly, to a protocol stack for providing data communication between communication application entities.
2. Description of the Related Art
Generally, a transmitter refers to as an apparatus for linking two transmitters or for linking a switching system to a subscriber. Such transmitter is mainly classified into two types: a radio transmitter and a cable transmitter. There are numerous types of cable transmitters such as optical transmitters used to transmit and receive the optical signals. The optical transmitters provide data link connection through optical links between two transmitters, a switching system and a transmitter, or a transmitter and a plurality of subscribers. These types of optical transmitters using the optical links communicate the data through data communication channel (DCC). Now, reference will be made as to the optical transmitter in connection with FIG. 1.
A transmitter 10 is linked to another transmitter 20 via an optical link. Data are processed by the data channel processors 11 and 21 provided in the transmitters 10 and 20, respectively, and communicated between the transmitters 10 and 20. As these two transmitters have the same construction, a description will be made depicting only the transmitter 10 as an illustrative example. First, the data channel processor 11 having a plurality of slave processors 12a, 12b, . . . , and 12n coupled thereto in the lower application layer controls the traffic flow of the data communication to and from another data channel processor 21 as well as the slave processors 12a, 12b, . . . , and 12n. The type and the number of the slave processors are dependent on the processing capacity of the transmitter 10. For example, a 2.5 Gbps transmitter would have four slave processors and the processing rate for each slave processor would be 622 Mbps. These slave processors are further linked to other information processing equipment or subscriber via optical links. The slave processors are usually linked to the data channel processor 11 through Ethernet. The data channel processor 11 of the transmitter 10 is provided with a protocol stack module that specify the physical media, the manner, and the process for conducting the data communication. Each of the slave processors 12a, 12b, . . . , and 12n is also provided with its own protocol stack. A description will be made below with reference to FIG. 2 as to the protocol stacks of the data channel processor 11 and the slave processors 12a, 12b, . . . , and 12n. 
The data channel processor 11 has a protocol stack of a seven-layer model as set forth in the OSI (Open System Interconnection) Basic Reference Model. More specifically, the data channel processor 11 includes an application layer 31 as the highest layer which contains a CMIP (Common Management Interface Protocol) for exchanging data between the application entities, an ROSE (Remote Operation Service Element) for a remote operation service by providing request/reply transaction in situations where a long-term association between the application entities is required, and an ACSE (Association Control Service Element) for transporting Call Detail Records to a centralized administrative center.
The lower layers of the application layer 31 are as follows. A presentation layer 32 has an ASN.1 (Abstract Syntax Notion 1) associated with the statement of a language used. The syntax is only concerned with the representation of the data and not the meaning to the application layer. A session layer 33 employs an X.225 standard for managing the data exchange between the application entities. A transport layer 34 serves to control the transfer of data between the entities, and a network layer 35 serves to perform the routing process to establish, maintain, and terminate the network connection. A data link layer 36 is divided into one section using an LAPD (Link Access Procedure of D-channel) and another section for an LLC1 section. The LLC1 section is linked to the slave processors for the data processing function. The LAPD section is further divided into a first subnet for data communication in the east direction of the data channel processor 11 and a second subnet for data communication in the west direction of the data channel processor 11. Accordingly, the data link layer 36 provides functional and procedural means to establish, maintain, and release the data link connections among network entities. Lastly, a physical layer 37,which is the lowest layer, has a section for the east/west data processing through optical links, and 10 Base 2 Ethernet is provided therein for data communication. The physical layer 37 is mostly a hardware dependent layer in OSI which provides mechanical, electrical, functional and procedural means to activate, maintain and de-activate a physical connection for data transmission between data link entities.
The individual slave processors 12a to 12n include a network layer 41, a data link layer 42, and a physical layer 43. The data link layer 42 is divided into two sections, LAPD and LLC1. The configuration of the data link layer 42 is similar to the data link layer 36 of the data channel processor 11. In the case that a 2.5 Gbps optical transmitter is employed, the LAPD would have one slave DCC and four subnets, each with 622 Mbps processing capability, and coupled to different information processing units.
As illustrated in the foregoing, each of the slave processors in a transmitter includes the OSI 7-layer protocol stack. However, such implementation has disadvantages in that the software cost rises as each slave processor incorporates its own protocol stack. That is, the cost increases as more protocol stacks are added to the system. Also, as each of the data channel processor and the slave processors is provided with its own protocol stack module in a given transmitter, the transmitter with one node has to have two network service access points (NASPs). This makes an operator or the system to perform the unnecessary functions by assigning two network service access points to one node. The two network access points assigned to one node causes the system to have different addresses depending on which data channel processor and slave processor is connected to the node. As a result, the operator experienced more hardship and confusion in managing and maintaining such system. Furthermore, as two different addresses are assigned to one node and the structure is formed as if one node occupies two nodes, it leads to an increase in the number of nodes of the network, which in turn increases the load of the network. This is because the respective protocol stacks have to exchange a large amount of data mutually while communicating the different routing information, and the increase in the number of nodes requires more data to be processed, thereby increasing the load of the network.
Moreover, as more software is implemented than necessary in each of the slave processors, more man power and more time is consumed in developing new programs. Further, the manufacturing cost of the system device is increased as more memory in the system devices, such as DRAM, SRAM of FROM, for the development of the programs is needed. Furthermore, the data channel processor is linked to the slave processors via Ethernet, which is the same network as that used by a graphic user interface (GUI) for providing the interface between a network management subsystem (NMS) and an operator. As the system experience heavy load owing to the data communication between two processors, the system experience more load on the system when using GUI or NMS.
As described above, using the OSI 7-layer protocol stacks separately in both the data channel processor and the slave processors of the transmitter causes the following problems: (1) the cost of software is increased; (2) it is difficult to manage the addresses since two addresses are assigned to one node; (3) one node is operated in the same manner as having two nodes to increase the load to the system; (4) a lot of software requirements in the slave processors demand more hardware, i.e. memories, thereby increasing the manufacturing cost of the system devices; and, (5) the network experiences an increase in the load of the system and thereby restricted to use limited services.
It is, therefore, an object of the present invention to provide a low-cost data communication channel processing device not limiting other services and not assigning two addresses to one node by constructing a protocol stack only in the data channel processor, and a method for operating the data communication processing device.
To achieve the above object of the present invention, there is provided a method for constructing a protocol stack of a data channel processor in a transmitter, the protocol stack comprising an application layer having a common management interface protocol (CMIP), a remote operation service element (ROSE), and an association control service element (ACSE); a presentation layer having an abstract syntax notion 1 (ASN.1) associated with the statement of an employed language; a session layer using an X.225 standard for managing data exchange; a transport layer for transferring data; a network layer for conducting a routing function; and, a plurality of subnets for communicating the data. Here, the plurality of subnets includes the first and the second subnets which serve to communicate the data with the system in the first and the second directions opposite each other, and the remaining subnets serve to communicate the data with the slave processors.
In another aspect of the present invention, there is provided a data communication channel processing apparatus for a transmitter comprising a data channel processor having a protocol stack for communicating the data with slave processors through a DPRAM (Dual Port Random Access Memory); the slave processors including tasks for recording the data received via an optical link in the DPRAM, reading the data from the DPRAM, and outputting the data to the optical link; and, the DPRAM for recording the data output from the slave processors or the data channel processor and communicating the data between the slave processors and the data channel processor.
Another object of the present invention is to provide a computer-readable memory medium for storing computer-executable process steps in a data channel processor to process data between the data channel processor and a plurality of slave processors, wherein the medium includes an accessing step and a driving step, the computer-executable process steps comprising: (1) the accessing step comprising the steps of: a generating step for outputting a provision signal prior to data transmission to the driving step to set the driving step in a receiving mode; a downward processing step that activates, maintains, and de-activates a physical connection for the data transmission to the slave processors; and, an upward processing step that activates, maintains, and de-activates a physical connection for the data transmission to the data channel processor; (2) the driving step comprising the steps of: a transmitting step for transmitting the data to another data channel processor; a downward driving step for receiving the data from the downward processing step and for recording the received data in a Dual Port Random Access Memory (DPRAM); and, an upward driving step for reading the recorded data from the DPRAM and outputting the read data to the upward processing step.
A further object of the present invention is to provide a computer-readable memory medium for storing computer-executable process steps in a plurality of slave processors coupled to other devices via a plurality of optical links to process data between a data channel processor and the slave processors, the computer-executable process steps comprising: an inputting step for reading the data transmitted from the data channel processor and stored in a Dual Port Random Access Memory (DPRAM) during a downward processing mode; a distributing step for transmitting the read data from the DPRAM to corresponding the other devices via the slave processors during the downward processing mode; a collecting step for combining the data received from the other devices via the plurality of the optical links and for storing the combined data in the DPRAM during an upward processing mode; an outputting step for outputting the combined data stored in the DPRAM to transmit the combined data to the channel data processor during the upward processing mode; and, a synchronizing step for matching the configuration between the inputting step and the outputting step so that the execution of the outputting step can perform synchronously with the inputting step.